The present invention generally relates to rotary recording mediums and reproducing apparatuses therefor, and more particularly to a rotary recording medium from which a fine still picture reproduction and normal reproduction can be performed selectively, and in which a scanning locus of a pickup reproducing element upon normal reproduction is unitarily determined so that normal reproduction can be performed accurately with respect to a desired track, and a reproducing apparatus for reproducing such rotary recording medium.
An information signal recording and reproducing system has been previously proposed in which the recording system forms pits in accordance with the information signal to record the information signal along a spiral track on a flat rotary recording medium (hereinafter simply referred to as a disc), without forming a groove therein. In the reproducing system, a reproducing stylus traces over along this track to reproduce the recorded information signal in response to variations in the electrostatic capacitance formed between a reproducing stylus and the disc.
In this previously proposed system, since no grooves are provided on the disc for guiding the reproducing stylus, it becomes necessary to record pilot or reference signals on or in the vicinity of a track of the information signal such as a video signal, on the disc. Upon reproduction, the reference signals are reproduced together with the video signal. Tracking control is carried out so that the reproducing stylus accurately traces along the track in response to the reproduced reference signals.
By use of this previously proposed system, there is no possibility whatsoever of the reproducing stylus or the disc being damaged, since the recording track has no groove. The reproducing stylus can trace the same portion of the track repeatedly many times, whereby a special reproduction such as still, slow-motion, or quick-motion picture reproduction becomes possible.
In the above type of a disc, a standard is set for the above proposed system so that four fields of video signal is recorded for one track turn of the disc. This standard was set in order to increase the recording capacity under the restricting conditions introduced by the practical diameter and rotational speed of the disc, the relative linear speed between the reproducing stylus and the disc for obtaining a fine signal-to-noise (S/N) ratio, and the like.
When a still picture reproduction is performed with the above disc, the same track turn is reproduced repeatedly. Accordingly, the video signal of four fields is repeatedly reproduced in this case, to perform the still picture reproduction. However, if the picture content of the video signal which is to be reproduced is a moving picture, the picture recorded in one track turn becomes different in each of the four fields. As a result, the picture obtained by the above still picture reproduction is not completely still, and the picture appears to undergo a reciprocating movement. Hence, as the movement in the above moving picture becomes faster, the reciprocating movement in the still picture reproduction picture increases. Therefore, there is a disadvantage in that the still picture reproduction picture does not appear still, and is unpleasant to watch.
On the other hand, another system may be considered wherein the same video information content is repeatedly recorded in four fields in one track turn, and the still reproduction is performed by repeatedly reproducing the same one track turn. In this case, even if the same one track turn is repeatedly reproduced, the still picture reproduction picture is completely still, because only the same video information content is repeatedly reproduced from the four fields constituting the above one track turn.
If the above disc is repeatedly recorded with the video information of the first field throughout the four fields in the first track turn, repeatedly recorded with the video information of the fifth field throughout the four fields in the succeeding track turn, and thereafter similarly repeatedly recorded with the same video information throughout the four fields in one track turn, the still picture reproduction picture obtained is completely still. However, because 3/4 of the video information is missing, there is a disadvantage in that the movement in the reproduced picture is not smooth upon normal reproduction.
On the other hand, the disc may be repeatedly recorded with the video information of the first field throughout the four fields in the first track turn, repeatedly recorded with the video information of the second field throughout the four fields in the succeeding track turn, and thereafter similarly repeatedly recorded with video information of each field throughout the four fields in one track turn without missing any video information. When reproducing such a disc, a complete still reproduction picture can be obtained. However, upon normal reproduction, the video information in each field is reproduced four times, and the reproduced picture becomes a slow-motion reproduction picture. Moreover, in discs capable of providing complete still reproduction picture, there is a disadvantage in that a normal audio signal cannot be obtained.
In order to overcome the above described problems, a disc and reproducing apparatus therefor was proposed in a U.S. patent application entitled "ROTARY RECORDING MEDIUM AND REPRODUCING APPARATUS THEREFOR" in which the assignee is the same as that of the present application. In this proposed disc and reproducing apparatus, the disc is repeatedly recorded with a video signal of the same unit for a plurality of field periods in each track turn, and divided audio signal parts obtained by dividing an audio signal in units of field periods of the video signal which is to be reproduced are successively arranged and recorded on a recording track of the video signal according to a tracing locus of a reproducing element on the disc upon normal reproduction during which change of track is performed by forcibly shifting the reproducing element at least once or a plurality of times for two revolution periods of the disc. Thus, the disc reproducing apparatus can obtain a complete still reproduction picture by repeatedly reproducing the video signal of the same unit in one track turn upon still picture reproduction. Upon normal reproduction, fine normal reproduction picture and reproduced normal audio signal can be obtained, by forcibly shifting the reproducing element to another track at a predetermined position on the disc.
However, the reproducing element may be forcibly shifted to another track at a position other than the original shifting position upon normal reproduction. In such a case, the normal reproduction picture and the reproduced normal audio signal are poorly obtained. Furthermore, the video signal recorded on one recording surface of the disc is usually not from the same kind of video signal source. That is, a video signal from another kind of video signal source is often mixed into the video signal from one video signal source. For example, when recording an educational program, the picture corresponding to a part where a teacher and the like comments, is obtained from a reproduced video signal from a magnetic recording and reproducing apparatus. On the other hand, the picture corresponding to a part where the comments are finished and the contents are described concretely, is obtained from a video signal from a movie film, for example. In this case, the recording method for the video signal which is normally reproduced, differs according to the video signal source. Hence, it becomes necessary to change the scanning locus of the reproducing element according to the kind of video signal source. However, it is difficult to cause the reproducing element to scan over a scanning locus in accordance with the video signal source, without specific information thereof.
The disc may be recorded with a video information on one recording surface, where the video information time serially composed of two different video information. One video information may be a video information to be reproduced with a picture arbitrarily selected from a still reproduction picture and a normal reproduction picture, and the other video information may be a video information to be reproduced only as a normal reproduction picture. For example, in a program containing a golf tournament, the picture corresponding to the part where the player makes a shot is a video information which can be either obtained as a still reproduction picture or a normal reproduction picture, and accordingly reproduced with the arbitrarily selected picture from the still reproduction picture and the normal reproduction picture. On the other hand, the picture corresponding to a part where the player walks to his golf ball need not be reproduced as a still picture, and thus is a video information which is to be obtained only as a normal reproduction picture. When reproducing such a disc, it is highly desirable to obtain a normal reproduction picture in which the movements are natural. This may be realized if the reproducing apparatus can automatically discriminate the tracks recorded with the video information which is to be obtained as either one of the selected still reproduction picture and the normal reproduction picture, and the tracks recorded with the video information which is to be obtained only as the normal reproduction picture.